It is costly to deliver containers, such as Front Opening Unified Pods (FOUPs) and Standard Mechanical Interface (SMIF) pods, to processing tools and load ports in a semiconductor fabrication facility. One method of delivering FOUPs between processing tools is an overhead transport (OHT) system. The OHT system lowers a FOUP onto the kinematic plate of the load port at approximately 900 mm height from the fabrication facility floor. An OHT system uses sophisticated ceiling mounted tracks and cable hoist vehicles to deliver FOUPs to, for example, a load port of a processing tool. The combination of horizontal moves, cable hoist extensions, and unidirectional operation, must be coordinated for transporting FOUPs quickly between processing tools. A transport vehicle must be available at the instant when a processing tool needs to be loaded or unloaded for best efficiency.
OHT systems are often mounted on portions of a facility ceiling, and therefore, are located above the processing tools and load ports. OHT systems utilize free space in the fabrication facility as the processing tools are typically floor mounted equipment. Ceiling mounted OHT systems must raise or lower a container a substantial distance between the OHT track and, by way of example only, a load port. An OHT system preferably has a very high cleanliness performance because any particles created from moving FOUPs along the track may fall onto the tool areas located underneath and potentially damage wafers.
Rail guided vehicles (RGVs) and automatic guided vehicles (AGVs) are often utilized in semiconductor fabrication facilities to move containers along the facility floor between processing tools. RGV's and AGV's are easier to access for maintenance purposes than an OHT system and are typically less costly than ceiling mounted OHT systems. Particle control is also simplified because particles generated by an RGV or AGV remain below the datum plane of a load port. RGVs and AGVs, however, occupy valuable floor space—which is at a premium in a semiconductor fabrication facility.
Wafer throughput could be improved in a semiconductor facility by delivering wafers to tools by both a floor-based transport system and an OHT system. For example, an OHT system could deliver the FOUP to a processing tool while the numerous container deliveries between adjacent processing tools are handled by a floor based transport system. This would be the case, for example, when process tools require that the first wafer of every FOUP be tested on a metrology tool in the bay.
Accordingly, there is a need for an improved FOUP delivery system in semiconductor fabrication facilities. The present invention provides a FOUP delivery system that reduces the cost of FOUP delivery, increases accuracy of FOUP delivery, simplifies installation and maintenance, improves the cleanliness performance and reduces delays associated with conventional FOUP transport systems.